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Update: Measles --- United States, January--July 2008

Sporadic importations of measles into the United States have occurred since the disease was declared eliminated from
the United States in 2000 (1). During January--July 2008, 131 measles cases were reported to CDC, compared with an average
of 63 cases per year during 2000--2007.* This report
updates an earlier reporton measles in the United States during 2008
(2) and summarizes two recent U.S outbreaks among unvaccinated school-aged children. Among those measles cases
reported during the first 7 months of 2008, 76% were in persons aged <20 years, and 91% were in persons who were
unvaccinated or of unknown vaccination status. Of the 131 cases, 89% were imported from or associated with importations from
other countries, particularly countries in Europe, where several outbreaks are ongoing
(3,4). The findings demonstrate that
measles outbreaks can occur in communities with a high number of unvaccinated persons and that maintaining high overall
measles, mumps, and rubella (MMR) vaccination coverage rates in the United States is needed to continue to limit the spread
of measles.

Measles cases in the United States are reported by state health departments to CDC using standard case
definitions and case classifications. Cases acquired outside the United States are categorized as importations. Those acquired inside the
United States are considered importation associated if they are linked epidemiologically via a chain of transmission to an
importation or have virologic evidence of
importation.§ Other cases are classified as having an unknown source. In the United
States, recommendations for MMR vaccination include a single dose at age 12--15 months and a second dose at the time of
school entry (5). Vaccination as early as age 6 months is recommended for U.S. children traveling abroad and is
sometimes recommended within U.S. communities during outbreaks of measles.

During January 1--July 31, 2008, 131 measles cases were reported to CDC from 15 states and the District of
Columbia (DC): Illinois (32 cases), New York (27), Washington (19), Arizona (14), California (14), Wisconsin (seven), Hawaii
(five), Michigan (four), Arkansas (two), and DC, Georgia, Louisiana, Missouri, New Mexico, Pennsylvania, and Virginia (one
each). Seven measles outbreaks (i.e., three or more cases linked in time or place) accounted for 106 (81%) of the cases.
Fifteen of the patients (11%) were hospitalized, including four children aged <15 months. No deaths were reported.

Among the 131 cases, 17 (13%) were importations: three each from Italy and Switzerland; two each from Belgium,
India, and Israel; and one each from China, Germany, Pakistan, the Philippines, and Russia. This is the lowest percentage
of imported measles cases since 1996 (Figure 1). Nine of the importations were in U.S. residents who had traveled abroad,
and eight were in foreign visitors. An additional 99 (76%) of the 131 cases were linked epidemiologically to importations or
had virologic evidence of importation. The source of measles acquisition of 15 cases (11%) could not be determined.

Among the 131 measles patients, 123 were U.S. residents, of whom 99 (80%) were aged <20 years
(Table). Five (4%) of the 123 patients had received 1 dose of MMR vaccine, six (5%) had received 2 doses of MMR vaccine, and 112 (91%)
were unvaccinated or had unknown vaccination status. Among these 112 patients, 95 (85%) were eligible for vaccination, and
63 (66%) of those were unvaccinated because of philosophical or religious beliefs
(Figure 2).

Washington. On April 28, 2008, the Washington State Department of Health received a report of several suspected
measles cases in a Grant County household. The index
patient had rash onset on April 12. During April 18--21, the other
seven children in the household became ill with fever and rash. Three of the children developed pneumonia and were evaluated by
a health-care provider who suspected measles; all three tested positive for measles-specific IgM antibody. Rash onset
occurred during April 13--May 30 in 11 additional cases identified in Grant County. All of the 19 cases were linked
epidemiologically, and all but one occurred in children and adolescents aged 9 months to 18 years. The 19 cases included 16 in
school-aged children, among whom 11 were home schooled. Because of their parents' philosophical or religious beliefs, none of the
16 children had received measles-containing vaccine. Specimens from eight patients were submitted for virologic testing, and
all contained genotype D5, which had been circulating in Japan and parts of Europe. A possible source of the outbreak was
a church conference, held March 25--29 in King County, Washington, that was attended by four of the patients, including
the index patient. The conference was attended by approximately 3,000 persons, primarily students from junior high
through university age from 18 states, DC, and several foreign countries. None of these countries or states has since reported
confirmed cases of measles among persons who attended this conference.

Illinois. On May 19, 2008, the Illinois Department of Public Health was notified by the DuPage County
Health Department about a suspected case of measles. By May 27, four confirmed cases of measles had been reported to the
county,
three of which were laboratory confirmed. Among the four cases, rash onsets occurred during May 17--19, suggesting
a common exposure. The four patients were unvaccinated girls aged 10--14 years; all had attended an event May 5 and
might have attended a home gathering 2 days earlier. Both events were attended by a teenager who had recently returned from
Italy and reportedly had developed fever and rash.
Although attempts to obtain further information about the traveler
were unsuccessful, viral isolation from one of the four patients yielded genotype D4, a strain circulating in Italy. Through July
31, 26 additional measles cases were reported, all with epidemiologic links to the first four cases. Among the 30 cases, 14
were confirmed in DuPage County, 11 in suburban Cook County, and five in Lake County. One case
occurred in a person aged 43 years. The remaining 29 cases were in persons aged 8 months--17 years, including 25 (83%) school-aged children, all
of whom were home schooled and not subject to school-entry vaccination requirements. Because of their parents' beliefs
against vaccination, none of the 25 had received measles-containing vaccine.

Editorial Note:

The number of measles cases reported during January 1--July 31, 2008, is the highest year-to-date since
1996. This increase was not the result of a greater number of imported cases, but was the result of greater viral transmission
after importation into the United States, leading to a greater number of importation-associated cases. These
importation-associated cases have occurred largely among school-aged children who were eligible for vaccination but whose parents chose not to
have them vaccinated. One study has suggested an increasing number of vaccine exemptions among children who attend school
in states that allow philosophical exemptions
(6). In addition, home-schooled children are not covered by
school-entry vaccination requirements in many states. The increase in importation-associated cases this year is a concern and might herald
a larger increase in measles morbidity, especially in communities with many unvaccinated residents.

In the United States, measles caused 450 reported deaths and 4,000 cases of encephalitis annually before measles
vaccine became available in the mid-1960s
(1). Through a successful measles vaccination program, the United States
eliminated endemic measles transmission (1). Sustaining elimination requires maintaining high MMR vaccine coverage rates,
particularly among preschool (>90% 1-dose coverage) and school-aged children (>95% 2-dose coverage)
(7). High coverage levels provide herd immunity, decreasing everyone's risk for measles exposure and affording protection to persons who cannot be
vaccinated. However, herd immunity does not provide 100% protection, especially in communities with large numbers of
unvaccinated persons. For the foreseeable future, measles importations into the United States will continue to occur because measles is
still common in Europe and other regions of the world. Within the United States, the current national MMR vaccine coverage
rate is adequate to prevent the sustained spread of measles. However, importations of measles likely will continue to
cause outbreaks in communities that have sizeable clusters of unvaccinated persons.

Measles is one of the first diseases to reappear when vaccination coverage rates fall. Ongoing outbreaks are occurring
in European countries where rates of vaccination coverage are lower than those in the United States, including Austria, Italy,
and Switzerland (3,4). In June 2008, the United Kingdom's Health Protection Agency declared that, because of a drop
in vaccination coverage levels (to 80%--85% among children aged 2 years), measles was again endemic in the United
Kingdom (3,8), 14 years after it had been eliminated. Since April 2008, two measles-related deaths have been reported in Europe,
both in children ineligible to receive MMR vaccine because of congenital immunologic compromise
(4,8).Such children depend on herd immunity for protection from the disease, as do children aged <12 months, who normally are too young to
receive the vaccine. Otherwise healthy children with measles also are at risk for severe complications, including encephalitis and
pneumonia, which can lead to permanent disability or death.

The measles outbreaks in Illinois and Washington demonstrate that measles remains a risk for unvaccinated persons
and those who come in contact with them
(9,10). Each school year, parents should ensure that their children's vaccinations
are current, regardless of whether the children are returning to school, attending day care, or being schooled at home.
Adults without evidence of measles
immunity¶ should receive at least 1 dose of MMR vaccine. All persons who travel
internationally also should be up-to-date on their measles vaccination and other vaccinations
recommended for countries they might visit. These recommendations include a single dose of MMR vaccine for infant travelers aged 6--11 months and
2 doses, administered at least 28 days apart, for children aged
>12 months (5).

 CDC/Council of State and Territorial Epidemiologists measles clinical case definition: an illness characterized by a generalized maculopapular rash for
>3 days, a temperature of >101°F
(>38.3°C), and cough, coryza, or conjunctivitis. A case is considered confirmed if it is laboratory confirmed (using serologic or
virologic methods) or if it meets the clinical case definition and is epidemiologically linked to a confirmed case.

§ A case is considered to have virologic evidence of importation if it is within a chain of transmission from which a measles virus is identified that is not endemic
in the United States.

¶ Documented receipt of 2 doses of live measles virus vaccine, laboratory evidence of immunity, documentation of physician-diagnosed measles, or birth
before 1957.

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